A conventional paint or solvent application booth provides a fully or partially enclosed, climate controlled space in which workpiece(s) may be spray coated or otherwise treated. In typical paint spraying operations, the operator stands in the vicinity of the workpiece(s) and applies the coating with a paint atomizing system. Forced ventilation air is passed through the booth, picking up paint overspray particulate and solvent vapors. The minimum ventilation air flowrate is prescribed, by law or regulation, based on the type of paint application system used (i.e. air atomized, airless, or electrostatic spray application). Typically, a linear velocity of 100 feet per minute (fpm) is employed in spray booths. The ventilation air then passes through a particulate emission control system (PECS) prior to being exhausted to the outside atmosphere. The PECS is known in the art. In most cases, the PECS utilizes either a water curtain or dry filter system to remove the paint overspray particulate. The solvent vapor contained in the exhaust air is not removed by the PECS, and therefore is often exhausted without any control.
In many instances solvent emissions from paint or solvent spray operations must be controlled to an acceptable level, as required, for example, by law or regulation. However, for many booth operators, the costs of installing and operating an appropriate solvent, or volatile organic compound (VOC), emission control device are prohibitive. High control costs are due primarily to the high paint booth exhaust flowrates (10,000 cubic feet per minute (cfm) to 1,000,000 cfm, or higher) containing low solvent concentrations that typify painting operations. Furthermore, VOC emission control device must be large enough to process the entire booth exhaust air flow. The invention described herein provides a method for controlling paint booth VOC emissions.
U.S. Pat. No. 4,266,504 discloses a paint spraying booth assembly including a VOC emission control device in which part of the exhaust air is processed without differentiating its levels of solvent concentrations.